1. Field of the Invention:
This invention relates to certain selenium compounds, a method for their preparation and, in particular, to selenium compounds having applications in competitive protein binding assays such as immunoassays.
2. Brief Statement of the Prior Art:
Competitive protein binding assay, e.g., immunoassay, is a recent development wherein known quantities of labeled and unlabeled antigen binding reactants, such as a hormone, are admixed with a protein, e.g., antibody, and the resultant product is analyzed for the concentration of bound or unbound labeled antigen or hapten to determine reactant concentrations, reaction kinetics and the like. The procedure has been widely used in an application known as radioimmunoassay to measure biological concentrations of materials in blood and urine such as digitalis glycosides, morphine, vitamins, enzymes, other proteins, polypeptides and viruses.
A material which is widely used in radioimmunoassay is the Bolton-Hunter reagent. This material is the N-hydroxysuccinimide ester of iodinated p-hydroxyphenylpropionic acid. The radioactive isotope of iodine (.sup.125 I) is used in the radioassay. In typical applications with this material a standard preparation of unlabeled hormone and plasma, serum or urine sample to be assayed are admixed with identical quantities of hormone labeled with the above-mentioned reagent and specific antibody. The antibody competes with labeled and unlabeled hormones in a competitive binding reaction. The resultant mixture is treated to separate the free from the bound hormone and the separated portions are then analyzed for radioactivity to determine the ratio between the bound and unbound hormone for the purpose of hormone quantitation.
The aforementioned Bolton-Hunter reagent has a number of disadvantages which limit its applications. The half-like of the iodine (.sup.125 I) is 60 days, and the reagent, therefore, requires iodination shortly prior to its use. The iodine is bound to a bulky hydroxyphenyl group which limits, to some extent, the reactivity with antibody and reagent labeled antigens and haptens. The bulky organic portion of the compound also renders the compound somewhat hydrophobic and this also limits its immunologic reactivity, specificity, and applications. Finally, the Bolton-Hunter reagent requires the employment of an unstable radioactive iodine tracer, (.sup.125 I), and it is most desirable to provide a small molecular tracer reagent that will bind to antigens, haptens and antibodies and permit simple, nonradioactive analysis such as fluoroassays.